Microwave power dividing network



Jan. 14, 1969 Filed Feb. 24, 196'? Sheet of2 RANGE OF OPERAT/Q/V I i 24' I V H B/AS/IVG MAGNET/C F/ELD lNl/ENTOR M. OMOR/ A 7'7'ORNEV Jan. 14, 1969 sAHl o QMORI 3,422,375

\ MICROWAVE POWER DIVIDING NETWORK Filed Feb. 24, 1967 Sheet 2 0f 2 FIG. 4

45 PORT 0) 7 PORT (a) E Em/wt E t a E I I 46 s/N-( +45) VOLTAGE United States Patent 3,422,375 MICROWAVE POWER DIVIDING NETWORK Masahiro Omori, Allentown, Pa., assignor to Bell Telephone Laboratories, Incorporated, Murray Hill, Berkeley Heights, N.J., a corporation of New York Filed Feb. 24, 1967, Ser. No. 618,460 US. Cl. 333--1.1 Claims Int. Cl. H01p 1/32 ABSTRACT OF THE DISCLOSURE A coupling network that has power division properties enough like those of hybrid junctions and directional couplers to substitute therefor in integrated strip line microwave circuits. A four port strip line junction is loaded both with a polarized body of gyromagnetic material and a conductive body both proportioned so that a circularly polarized mode as well as a static mode can be equally supported at the same resonant frequency. Interaction of these modes at the several ports produces unusual coupling characteristics.

BACKGROUND OF THE INVENTION The invention relates to microwave power dividing networks and more particularly to a network adapted for strip line construction which has properties similar to hybrids and directional couplers.

Waveguide and coaxial line directional couplers and hybrid junctions are familiar forms of microwave power dividing networks. While these components are stable and dependable they are physically cumbersome, expensive to fabricate and are not easily integrated with the strip line and printed circuit forms of high frequency wave transmission line now being extensively used. On the other hand, the microwave circulator has been developed to the point where its strip line construction is simple and inexpensive and is generall considered the preferred circulator form. From one aspect the present invention may be viewed as a coupling network having some of the properties of hybrid junctions or directional couplers but having the physical simplicity of a strip line circulator. From another aspect the invention could be viewed as a modified strip line circulator having properties more nearly like hybrids or directional couplers.

SUMMARY The structure according to one embodiment of the invention resembles a four port strip line circulator having a conductive center post, shorting the center conductor to both ground planes. This post is large enough to allow a static, transverse magnetic field mode (TM to develop circumferentially about the post, that, for a particular strength of magnetic biasing, is resonant at the same frequency and with the same loaded Q as one of the circularly polarized transverse magnetic modes (TM+ and TM previously used in circulators of this type. Constructive and destructive interference of the two resonant modes produces a power division between the two ports adjacent to the one excited and power isolation at the port opposite to the one excited similar to the power division found useful in hybrid junctions. The relative phase shift between the divided components is 90 degrees, as in a directional coupler or a 90 degree hybrid, but lags and leads, respectively, the exciting power by 45 degrees in a nonreciprocal manner that depends upon the direction of the biasing field. It is therefore apparent that neither the comparison to the circulator nor to the hybrid is strictly complete, since the network of the present invention has properties found in neither of these prototypes. Its greatest potential usefulness, however, is

ice

expected to be realized as a substitute for hybrids in integrated strip line assemblies.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a strip line power dividing network in accordance with the invention;

FIG. 2, given for the purpose of explanation, is a plot of the resonant frequency vs. biasing magnetic field of transverse magnetic modes supported in the structure of FIG. 1 and illustrates the condition of operation in accordance with the invention;

FIGS. 3a through 3c each illustrate the hybrid mode patterns and their equivalent combination at different times in the structure of FIG. 1; and

FIG. 4 diagrams the phase and amplitude of power division in the structure of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring more particularly to FIG. 1, it will be seen how the basic structure of the invention superficially resembles a four port strip line junction circulator described, for example, in the article by Fay & Comstock, Operation of the Ferrite Junction Circulator, 13 IEEE Transactions MT&T, January 1965 pages 15 through 27. Thus, the particularly illustrated embodiment includes a pair of flat electrically conductive ground plane members 10 and 11 extending parallel to and spaced apart from each other. Conductive side walls such as 7 and 9 connect and support ground planes 10 and 11 and while illustrated as forming a rectangular cavity, can form an enclosure of arbitrary size and shape.

Centrally spaced between and parallel to ground plane members 10 and 11 is a center conductor or spider member 12. This spider member includes a common portion and four portions or strips, such as 13, 14, 15 and 16, symmetrically extending at right angles to each other away from the common portion. These strips extend to openings in the side Walls and constitute input and/or output ports (1), (2), (3) and (4) of the network to which other strip lines, coaxial components, waveguides or loads may be connected by way of transition members conventional in the art. Discs 17 and 18 of magnetically polarized gyromagnetic material, such as yttrium iron garnet or ferrite, are located above and below the com: mon portion of spider 12 in accordance with the usual construction of Y-junction circulators. Discs 17 and 18 are then biased by being permanently magnetically polarized or are polarized by the use of external magnets as schematically represented by the vector H to the degree to be defined hereinafter.

Departing from the usual construction of circulators, the network in accordance with the present invention includes a conductive post 20 extending through holes in the centers of ferrite discs 17 and 18 and conductively connected to ground planes 10 and 11 and to the center of common portion of spider 12. In a typical embodiment post 20 has a diameter that is in the order of three tenths to six tenths of the diameter of common portion of spider 12 but in all cases selected for a given biasing field so that the two lowest order transverse magnetic modes TM and TM can be supported within the structure at substantially the same resonant frequency equal to the desired operating frequency of the network and that both modes have the same loaded Q at this frequency.

Referring to FIG. 2, curves 21 and 22 will be recognized as the resonant frequency vs. biasing magnetic field characteristics of the positive and negative rotating forms, respectively, of the circularly polarized TM mode commonly used in Y-junction circulators. The respective resonant frequencies (cavity resonance not gyromagnetic resonance) of these modes depend upon the permeability presented to each by ferrite members 17 and 18 and because of the tensor nature of this permeability, split as the biasing field is increased.

Curve 23 represents the resonant frequency of the TM mode which, in addition to depending upon biasing field, depends upon the size of post 26 (which has little effect upon the TM modes except to distort the field distribution around the post). Range 24 represents the conditions required for the present invention such that the TM curve intersects only one of the TM curves (TM being selected in the illustration) at the operating frequency w and the biasing field H Increasing the size of post 20 will cause curve 23 to move up in frequency and decreasing the size of post 20 will cause curve 23 to move down in frequency. In addition the diameter of post 20 should have such a ratio to the diameter of the common portion of spider 12 that the loaded Qs of the two modes are equal. With equal Qs, power applied to any of the ports will divide equally between the TM and TM mode. The TM mode is not used in the present example. Since its frequency of resonance is much above that of the applied energy, it will not be excited. It should be understood, however, that operation with the TM mode to the exclusion of the TM- mode is possible and is in general similar to the operation here described.

The shaded area 24 has been referred to as a range of operation, since even though curves 22 and 23 cross for discrete values of frequency and biasing field, mode pulling produces operation over a band of frequencies without adjustment of the field. It will be recalled that the same is true of junction circulators operating in a range midway between curves 21 and 22 at low values of biasing field as shown for example in the above-noted publication of Pay et al.

Operation, of a structure so proportioned may now be analyzed with the aid of FIGS. 3a through 31:. The first two symbol of each, such as 31 and 32 of FIG. 3a, show the separate field patterns respectively of the TM and TM The third symbol of each, such as 33 of FIG. 3a, shows the summed contribution of the fields from the first two symbols at each of the output ports (1), (2), (3) and (4). The individual FIGS. 3a, 3b and represent instantaneous views of these patterns at successive times respectively 45 degrees apart at the operating frequency.

Particularly, an input signal in the form E sin an applied to port (1) will have a maximum amplitude E at the time corresponding to wt=90 degrees and will divide as represented by the dotted connection 34 between the two modes as described so that each mode represents half the voltage amplitude at port (1). The TM mode has a rotating field pattern which at the time of FIG. 3a is represented by symbol 31 producing a voltage E/2 at port (2) with ports (3) and (4) both at voltage nulls. The TM mode has a static or nonrotating pattern represented by symbol 32 producing a voltage E/ 2 at all ports. The combined contribution of both modes at each port as shown in symbol 33 duplicates the applied voltage E at port (1), indicates a division with E/2 at adjacent ports (3) and (4), and shows that the separate mode contributions cancel at port (2).

At wt=l35 degrees, degrees later than the time of FIG. 3a, the modes appear as in FIG. 3b. The applied voltage which is decreasing from E in a sinusoidal manner is now E/ /2 and one half of it is applied to each mode as indicated by connection 35. Since the TM mode is rotating counterclockwise at its resonant frequency, its pattern shown by symbol 36 of FIG. 3b has turned 45 degrees as compared to FIG. 3a. The voltage at port 3 due to TM is now E/2 /2 and at ports 2 and (4) is E/2 /Z The TM mode contributes a voltage E/2 /7 at all ports as shown by symbol 37. The contribution of both modes as combined in symbol 38 produces E/Viat port (3) and zero at ports (2) and (4).

At wt=l degrees the input voltage at port (1) is zero. The resonant pattern of the rotating TM- mode is shown by symbol 39 of FIG. 3c and produces E/2 at port (3), -E/2 at port (4) and a null at port (2). The TM makes no contribution at any port as shown by symbols 40 and 41.

Other time positions repeat these patterns in other phases so that the resulting phase and amplitude at the several ports may be summarized in FIG. 4 for an input wave E sin wt of curve 45 at port (1). The power divides equally between ports (3) and (4) with that at port (3) shown by curve 46 leading the input by 45 degrees and expressed as E/x/2 sin (wl+45), and that at port (4) shown by curve 47 lagging the input by 45 degrees and expressed as E/ /2 sin (wt45). No power ever appears at port (2).

The network is, of course, symmetrical so that if power is applied to any other port, as for example, port (3), it will divide between ports (1) and (2) adjacent to port (3) with no power appearing at the opposite port (4). The relative phase of the divided power is degrees.

The power division to the extent described is similar to that of a directional coupler or a 90 degree phase shift hybrid and the network according to the invention can be used in substantially all applications in place of the more intricate components, particularly in strip line configurations. The relative phase of the divided power with respect to excited power is $45 degrees, the sense depending upon the sense of rotating of the TM- mode. To this extent the network is nonreciprocal, that is, it is equivalent to a hybrid with a nonreciprocal phase shift in each arm. These phase shifts combine so that the phase shift between any two ports is still nonreciprocal. Further, with shorts placed properly on the side ports, the device becomes a gyrator. Since the sense of this phase depends upon the direction of rotation of the TM- mode, which in turn can be reversed by reversing H the relative phase may be reversed. The usefulness of these additional properties will be readily envisioned by those skilled in the art.

While not illustrated in the drawing it should be understood that construction and impedance matching techniques familiar to the design of strip line circulators may be used with the invention. For example it is common practice as shown in the copending application of D. F. Linn, Ser. No. 479,439, filed Aug. 13, 1965 now Patent No. 3,323,079 to fill the region surrounding discs 17 and 18 with material of high dieletric constant in order to concentrate the magnetic fields. This dielectric is then often used as the support of the ground planes which eliminates conductive Walls 7 and 9. Further the Linn application discloses techniques for eliminating one of the ferrite discs 17 or 18 and alternatively for replacing the eliminated disc with a conductive body or a conductively bounded, permanently magnetized body.

The present invention has been illustrated in terms of strip line components since it is in this form that the invention is expected to have its principal usefulness. It should be understood however that a four port waveguide circulator can be adapted to support modes equivalent to the TM and TM modes here described and to produce a coupling characteristic identical to that defined.

In all cases it is to be understood that the abovedescribed arrangements are merely illustrative of a small number of the many possible applications of the principles of the invention. Numerous and varied other arrangements in accordance with these principles may readily be devised by those skilled in the art without departing from the spirit and scope of the invention.

I claim:

1. A coupling network for electromagnetic wave energy in a given frequency band comprising a wave guiding structure having four branches forming ports symmetrically extending away from a common region, a body of gyromagnetic material symmetrically disposed with respect to said common region, means for magnetically biasing said gyromagnetic material to a point at which wave energy in said given frequency band is resonant in a rotating transverse magnetic mode circularly polarized in one sense and remote from resonance in a rotating transverse magnetic mode circularly polarized in a sense opposite said one sense, means in said common region for producing resonance of said wave energy in a static transverse magnetic mode in said structure in said given frequency band and for dividing said wave energy applied to one of said ports between said mode rotating in said one sense and said static mode in a given amplitude and phase whereby said divided energy combines in another amplitude and phase at other ports.

2. A coupling network according to claim 1 wherein said structure comprises a center conductor member centrally disposed between and spaced in parallel relationship to a pair of ground plane conductors, wherein said magnetic biasing means produces resonance of a rotating TM mode circularly polarized in one sense in said given frequency band, and wherein said means for producing resonance of a static transverse magnetic mode includes a conductive body having such dimensions that a TM mode is also resonant in said structure for said magnetic bias in said given frequency band.

3. A coupling network according to claim 2 wherein said conductive body shorts the center of said common portion to both of said ground planes.

4. A coupling network according to claim 2 wherein said conductive body has a dimension parallel to said ground planes that is between three-tenths and six-tenths of the dimension of said common portion parallel to said ground planes.

5. A coupling network for electromagnetic wave energy in a given frequency band comprising a four port structure having a center conductor member centrally disposed between and spaced in parallel relationship to a pair of conductive surfaces, said center conductor member having four portions symmetrically extending away from a common portion, a body of gyromagnetic material symmetrically disposed with respect to said common portion, means for magnetically biasing said gyromagnetic ma terial to a point at which a rotating transverse magnetic mode circularly polarized in one sense is resonant in said structure in said given frequency band, a conductive body shorting the center of said common portion to said conductive surfaces, said conductive body having such dimensions that a static transverse magnetic mode is resonant in said structure with said magnetic bias and that wave energy in said band applied to one of said ports divides equally between said rotating mode and said static mode in said common portion, whereby said divided energy combines in other amplitudes at other ports.

References Cited UNITED STATES PATENTS 3,015,787 1/1962 Allin et a1. 333-1.1 3,174,116 3/1965 Sur 333-1.1

OTHER REFERENCES C. E. Fay et. al.: Operation of the Ferrite Junction Circulator, IEEE Trans. on MTT, January 1965, pp. 24- 27 relied on.

ELI LIEBERMAN, Primary Examiner.

P. L. GENSLER, Assistant Examiner.

US. Cl. X.R. 33311 

